Insulation materials comprising fibers having a partially cured polymer coating thereon, articles including such insulation materials, and methods of forming such materials and articles

ABSTRACT

Insulation materials have a coating of a partially cured polymer on a plurality of fibers, and the plurality of coated fibers in a cross-linked polymeric matrix. Insulation may be formed by applying a preceramic polymer to a plurality of fibers, heating the preceramic polymer to form a partially cured polymer over at least portions of the plurality of fibers, disposing the plurality of fibers in a polymeric material, and curing the polymeric material. A rocket motor may be formed by disposing a plurality of coated fibers in an insulation precursor, curing the insulation precursor to form an insulation material without sintering the partially cured polymer, and providing an energetic material over the polymeric material. An article includes an insulation material over at least one surface.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under Contract No.NMM11AA01B, Task Order NNM12AA33T, awarded by NASA, and Contract No. ABLW31P4Q-08-D-0026, awarded by the Army. The government has certain rightsin the invention.

TECHNICAL FIELD

Embodiments of the present disclosure relate to insulation materials,articles including the insulation materials, and methods of forming theinsulation materials and articles. Insulation materials of embodimentsof the present disclosure exhibit increased thermal resistivity comparedto conventional insulation.

BACKGROUND

Solid rocket motors include energetic and non-energetic materials.Improving the performance of a solid rocket motor typically requiresincreasing the performance of the energetic material, increasing themass of energetic material, decreasing the mass of the non-energeticmaterial, or some combination of these modifications. Because solidrocket motors are volume-limited systems, reducing the volume ofnon-energetic materials in the solid rocket motor allows for an increasein the volume and mass of energetic materials.

The non-energetic materials in a rocket motor may include, for example,a casing, insulation material, liner materials formulated to promotebonding, and nozzle materials. Reducing the volume of the insulationmaterial may leave a relatively larger volume within the rocket motor,but may also leave the casing with insufficient thermal protection.Thus, in the design of rocket motors, performance and thermal protectionare considered together in attempting to develop an optimized systemwithin known parameters.

Rocket motor casings are generally made of metal, a composite material,or a combination of metal and composite materials. During operation,insulation protects the rocket motor casing from thermal effects anderosive effects of particle streams generated by combustion of apropellant. Typically, the insulation is bonded to the interior surfaceof the casing and is fabricated from a composition that, upon curing, iscapable of enduring the high temperature gases and erosive particlesproduced while the propellant burns. A liner bonds the propellant to theinsulation and to any noninsulated interior surface portions of thecasing. Liners also typically have an ablative function, inhibitingburning of the insulation at liner-to-insulation interfaces.

The combustion of a solid rocket propellant generates extreme conditionswithin the rocket motor casing. For example, temperatures inside therocket motor casing can reach 2,760° C. (5,000° F.). These conditions,in combination with the restrictive throat region of the nozzlepassageway, create a high degree of turbulence of high-temperaturecombustion gases within the rocket motor casing and nozzle. In addition,gases produced during propellant combustion typically containhigh-energy particles that, under a turbulent environment such asencountered in a rocket motor, can erode the rocket motor insulation. Ifgases produced by the burning propellant penetrate the insulation andliner, the casing may melt or otherwise be compromised, causing therocket motor to fail. Thus, the insulation is formulated to withstandthe extreme conditions experienced during propellant combustion andprotect the casing from the burning propellant.

Some conventional rocket motor insulations include filled and unfilledplastics or polymers, such as phenolic resins, epoxy resins, hightemperature melamine-formaldehyde coatings, as well as ceramics,polyester resins, and the like. Plastics, however, tend to crack orblister in response to the rapid heat and pressure fluctuationsexperienced during rocket motor propellant combustion.

Rubbers and elastomers have also been used as rocket motor insulation.Cured ethylene-propylene-diene monomer (“EPDM”) terpolymer may be usedalone or in a blend, and is often selected because of its favorablemechanical, thermal, and ablative properties. However, in high-velocityenvironments, the ablative properties of elastomers are sometimesinadequate for rocket motor operation unless the elastomers arereinforced with suitable fillers, such as carbon fibers or silicafibers. The criticality of avoiding high erosion rates is demonstratedby the severity and magnitude of risk of failure due to erosion. Mostinsulation is, of necessity, “man-rated” in the sense that acatastrophic failure can result in the loss of human life. Additionally,the tensile strength and tear strength of unfilled elastomers may not besufficiently high to withstand and endure the mechanical stresses thatthe elastomer is subjected to during processing.

Incorporation of fibers can increase the ablation resistance of aninsulation material. However, many fibers are friable, and degradeduring the preparation of the insulation material.

It would be advantageous to provide a thermal protection system thatoccupies less volume than conventional insulation materials. Suchthermal protection may make it possible to increase the volume loadingof energetic material in a rocket motor, increasing the performance ofthe motor. Such thermal protection may also be useful to make advancedpropellant formulations feasible (e.g., propellants that burn hotterthan conventional propellants).

BRIEF SUMMARY

Some embodiments of the present disclosure include insulation materialshaving a plurality of fibers with a partially cured polymer coatingthereon and disposed in a cross-linked polymeric matrix.

Some methods of forming insulation materials include applying apreceramic polymer to a plurality of fibers, heating the preceramicpolymer to form a partially cured polymer over at least portions of theplurality of fibers, disposing the plurality of fibers in a polymericmaterial, and curing the polymeric material.

A method of forming a rocket motor includes coating a plurality offibers with a partially cured polymer formulated to form a ceramic uponexposure to a temperature of at least 850° C., disposing the pluralityof coated fibers in an insulation precursor, curing the insulationprecursor to form polymeric material without sintering the partiallycured polymer, and providing an energetic material over the polymericmaterial.

In some embodiments, an article includes an insulation material over atleast one surface. The insulation material includes a plurality offibers coated with a partially cured polymer, the plurality of coatedfibers dispersed in a cross-linked polymeric matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the invention,advantages of the present disclosure may be more readily ascertainedfrom the following detailed description when read in conjunction withthe accompanying drawings in which:

FIG. 1 shows a simplified schematic cross-section of an insulationmaterial according to an embodiment of the present disclosure;

FIG. 2 shows a simplified cross-section of an article including aninsulation material according to an embodiment of the presentdisclosure;

FIG. 3 shows a simplified cross-section of a rocket motor including aninsulation material according to an embodiment of the presentdisclosure;

FIG. 4 shows a simplified cutaway view of a rocket motor nozzleincluding an insulation material according to an embodiment of thepresent disclosure;

FIG. 5 shows a simplified schematic cross-section of the insulationmaterial of FIG. 1 after exposure to a temperature of greater than about850° C.;

FIG. 6 shows a simplified schematic cross-section of another insulationmaterial according to an embodiment of the present disclosure; and

FIG. 7 shows a simplified schematic cross-section of the insulationmaterial of FIG. 6 after exposure to a temperature of greater than about850° C.

DETAILED DESCRIPTION

Insulation materials, insulated articles, methods of forming insulationmaterials and insulated articles, and methods of firing rocket motorshaving the insulation materials are described. In one embodiment, aninsulation material includes fibers coated with a partially curedpolymer. The coated fibers are in a cross-linked polymeric matrix. Thecross-linked polymeric matrix may be a conventional insulation material.When the insulation material is exposed to high temperatures, such asthose that occur during a rocket-motor firing, the partially curedpolymer forms a ceramic on the insulation material that increases theinsulative properties of the insulation. The insulation material ofembodiments of the present disclosure may provide increased thermalprotection to an article containing the insulation material.

As used herein, the term “partially cured polymer” means and includes acrosslinked polymeric compound produced from a polymeric precursor of aceramic (a preceramic polymer). The partially cured polymer is formed bypartially curing the preceramic polymer at a temperature sufficient topromote crosslinking among carbons of the preceramic polymer but notsufficient to ceramify the preceramic polymer. The process of formingthe partially cured polymer may be referred to in the art as “staging,”“partially curing,” “polymerizing,” or “green-curing.” Thus, thepartially cured polymer is a material that has not been sintered to formceramic.

The insulation material may include a cross-linked polymeric material.The cross-linked polymeric material may be a cured solid, and mayinclude polymers used to form conventional insulation materials. Forexample, the cross-linked polymeric material may be polyisoprene, EPDMterpolymer, nitrile butadiene rubber (NBR), hydroxyl-terminatedpolybutadiene (HTPB) rubber, etc. The cross-linked polymeric materialmay also include a filler dispersed therein, such as silica, clay,carbon black, asbestos, or polyvinyl chloride. Depending on the desiredproperties, the insulation material may optionally include othercomponents, such as antioxidants, cure accelerators, cure activators,tackifiers, and/or plasticizers. Such components are known in the artand, therefore, are not described in detail herein.

The insulation material also includes a plurality of fibers within amatrix of the cross-linked polymeric material. The fibers are coatedwith the partially cured polymer. Fibers may be in bulk form(independent of one another) or in sheets of material (e.g., wovenfabric). The fibers may be, for example, aramid fibers (e.g., KEVLAR®brand fibers, available from E.I. du Pont de Nemours and Company, ofWilmington, Del.), carbon fibers, etc. The coated fibers may be withinthe continuous solid matrix of cross-linked polymeric material.

The partially cured polymer on the fibers may be a material formulatedto form a ceramic upon exposure to a relatively high temperature. Forexample, the partially cured polymer may form a ceramic, such as siliconcarbide, silicon nitrocarbide, or silicon oxycarbide, at a temperatureabove about 850° C., above about 1000° C., or even above about 1200° C.In its partially cured state, the partially cured polymer may have arubberlike consistency. Thus, the coating of the partially cured polymeron the fibers may be flexible until the partially cured polymer isceramified. Due to the high sintering temperature of the preceramicpolymer, the partially cured polymer may remain less than fully curedduring and after the continuous solid matrix is formed and cured. Forexample, in some embodiments, the continuous solid matrix may be formedby curing the cross-linked polymeric material at a temperature of about200° C. or lower, well below a sintering temperature of the partiallycured polymer. The partially cured polymer may include a silicon-based,preceramic polymer, such as an organosilicon polymer that produces asilicon carbide, silicon nitrocarbide, or silicon oxycarbide whenceramified. For example, the partially cured polymer may be apolycarbosilane, a polysilazane, a polysiloxane, or combinationsthereof. The partially cured polymer may be formed by a low-temperaturecure (e.g., a cure at a temperature from about 180° C. to about 400° C.)of the preceramic polymer. The preceramic polymer may be a liquid at atemperature at which the preceramic polymer is applied to the fibers.For example, the preceramic polymer may be a one-component liquidprecursor to silicon carbide, such as STARPCS® SMP-10, available fromStarfire Systems, of Schenectady, N.Y. Some preceramic polymers aredescribed in U.S. Pat. No. 7,714,092, issued May 11, 2010, and titled“Composition, Preparation of Polycarbosilanes and Their Uses.” Thecoating of the partially cured polymer may have a mean thickness overthe fibers of less than the mean diameter of the fibers. For example,the fibers may have a mean diameter from about 0.01 mm to about 1 mm. Insuch embodiments, the coating of the partially cured polymer may have amean thickness from about 0.001 mm to about 0.2 mm. Thus, the coating ofthe partially cured polymer may account for a small percentage of atotal weight of the insulation material.

FIG. 1 shows a simplified illustration of an insulation material 100.The insulation material 100 has a plurality of fibers 102 coated with apartially cured polymer 104. The coated fibers 108 are in a cross-linkedpolymeric matrix 106.

The insulation material 100 may be formed by coating fibers 102 with thepreceramic polymer (a first polymeric material), then heating the fibers102 and the preceramic polymer to a temperature sufficient to partiallycure or green-cure the preceramic polymer to form the partially curedpolymer 104. The preceramic polymer may be applied to the fibers 102 byconventional techniques, which are not described in detail herein. Thecoated fibers 108 may include a substantially continuous coating of thepartially cured polymer 104 over the fibers 102 or may include adiscontinuous coating of the partially cured polymer 104 over the fibers102. In some embodiments, the fibers 102 and the preceramic polymer maybe maintained at a temperature from about 100° C. to about 300° C., atatmospheric pressure, and less than about 10% relative humidity for atime period sufficient to polymerize the preceramic polymer. Forexample, the fibers 102 and the preceramic polymer may be maintained ata temperature of at least about 150° C. for a time period from about 30minutes to about 60 minutes. The degree of curing of the preceramicpolymer may be a function of the cure conditions (e.g., temperature,humidity, pressure, etc.) and the cure time. The coated fibers 108 maythen be mixed with or coated with a precursor of the cross-linkedpolymeric matrix 106, which may be a second polymeric material or amonomeric material. For example, the coated fibers 108 may be mixed witha precursor used to form polyisoprene, EPDM terpolymer, NBR, HTPBrubber, etc. In some embodiments, a sheet or cloth formed of the fibers102 may be coated with the partially cured polymer 104, then coated witha precursor of the cross-linked polymeric matrix 106. The coated fibers108 and the precursor may be heated to a temperature sufficient to curethe precursor to form the cross-linked polymeric matrix 106. The curetemperature may be selected such that the precursor cures withoutfurther curing, sintering, decomposing, or otherwise modifying thechemical structure of the partially cured polymer 104. In someembodiments, the precursor may be maintained at a temperature from about100° C. to about 300° C. in a press for a time period sufficient tocross-link or polymerize the precursor. For example, the coated fibers108 and the precursor may be maintained at a temperature of about 150°C. for a time period from about 30 minutes to about 60 minutes to formthe cross-linked polymeric matrix 106. A cure catalyst may be added tothe precursor to promote the curing thereof. The concentration of thecure catalyst may be tailored to effect formation of a material withselected physical properties (e.g., hardness, strength, ductility,etc.). The precursor may be cured in an oven maintained at approximatelyconstant temperature, pressure, and/or humidity.

The insulation material 100 may be applied to a surface (e.g., a surfaceof a rocket motor, a nozzle, or another body) after the insulationmaterial 100 is formed or the insulation material 100 may be applied toa surface in-situ. For example, the insulation material 100 may beformed into sheets, and the sheets may be bonded to a surface, or may bestrip-wrapped over a surface. In some embodiments, insulation precursors(e.g., a precursor to the cross-linked polymeric matrix 106 with coatedfibers 108 dispersed therein) may be applied to a surface, such as byspin-coating, spreading, etc., and the insulation precursors may becured to form the insulation material 100.

As shown in FIG. 2, an article 200 may include an insulation material202 (e.g., the insulation material 100 shown in FIG. 1) and an energeticcomposition 204 (e.g., a propellant composition, a gas generatorcomposition, a smokeless gun powder composition, a munitionscomposition, an explosive composition, etc.). The insulation material202 and the energetic composition 204 may be contained within a housing206 of the article 200. By way of example, the article 200 may include agas generating device, such as an airbag device or a fire suppressiondevice, ordnance, munitions, or a rocket motor. The article 200 may alsoinclude, but is not limited to, cartridges for small arms ammunition(e.g., rimfire cartridges, center fire cartridges, shot shells, rifledslugs, etc.), grenades, mines, mortar fuses, detcord initiators,illuminating flares, or signaling flares.

As shown in FIG. 3, a rocket motor 300 may include insulation materialsaccording to embodiments of the present disclosure. For example, arocket motor 300 may include a casing 302, an insulation material 304(e.g., the insulation material 100 shown in FIG. 1), a liner 306, and anenergetic material 308 (e.g., a solid propellant such as a double-basepropellant, an HTPB-based propellant, etc.). The insulation material 304may include the fibers coated with the partially cured polymer in thecured polymeric matrix. The rocket motor 300 may also include a nozzleassembly 310, an igniter 312, etc.

The rocket motor 300 may be formed by securing the insulation material304 within the casing 302 by conventional techniques. For example, theinsulation material 304 may be formed within the casing 302 or may beformed as one or more sheets, which are subsequently bonded to thecasing 302. The insulation material 304 may be formed as described abovewith respect to the insulation material 100 of FIG. 1. The liner 306 isprovided over at least a portion of the insulation material 304 and thecasing 302. The energetic material 308 is provided (e.g., cast) into thecasing 302 over the liner 306.

As shown in FIG. 4, a nozzle 350 may include insulation materialsaccording to embodiments of the present disclosure. For example, anozzle 350 may include an outer wall 352 and an insulation material 354(e.g., the insulation material 100 shown in FIG. 1). The outer wall 352may include a material formulated to provide physical structure overwhich the insulation material 354 is formed. For example, the outer wall352 may include a metal or a composite material. The insulation material354 may include the fibers coated with the partially cured polymer inthe cured polymeric matrix. For example, the insulation material 354 mayinclude a sheet or fabric of the fibers coated with the partially curedpolymer, and over which the polymeric matrix (e.g., a phenolic resin) isformed and cured.

The insulation materials 100, 202, 304, 354 disclosed herein and shownin FIGS. 1 through 4 may exhibit improved insulative properties whenexposed to temperatures sufficient to cause the partially cured polymer104 (FIG. 1) to form a ceramic. For example, when one side of theinsulation material 100 is exposed to a temperature sufficient to modifythe chemical structure of the partially cured polymer 104, a ceramic mayform. FIG. 5 illustrates an insulation material 400 that has beensubjected to a high temperature (e.g., greater than about 850° C.) alonga surface 402 of the insulation material 400. The insulation material400 has the fibers 102 coated with the partially cured polymer 104 inthe cross-linked polymeric matrix 106, as shown in FIG. 1 and describedabove. Following exposure to the high temperature, the insulationmaterial 400 forms two regions: a heat-affected region 401 and a virginmaterial region 403. The heat-affected region 401 may include twosub-regions: an ablated region 401 a and a char region 401 b. Theablated region 401 a may include ash that is easily removed from theinsulation material 400. The char region 401 b may include a crust ofmaterial that is adhered to the virgin material region 403. A portion ofthe cross-linked polymeric matrix 106 in the ablated region 401 a may beremoved during exposure to the high temperature. Furthermore, a portionof the partially cured polymer 104 in the heat-affected region 401reacts or fuses to form a ceramic 404 over or around the fibers 102. Theceramic 404 provides additional insulative properties to the insulationmaterial 400.

Since the partially cured polymer 104 includes a silicon-basedpreceramic polymer, the ceramic 404 formed during exposure of theinsulation material 400 to a high temperature may be an inorganicceramic, such as a glass material. In some embodiments, the ceramic 404may include silicon dioxide, silicon carbide, or a combination thereof.The ceramic 404 may be substantially free of carbon. In someembodiments, the ceramic 404 may include some carbon, but inorganicmaterials of the ceramic 404 may form a sintered matrix. The ceramic 404may be tenacious in that it remains adhered to the insulation material400 during use and operation of an article, such as the article 200(FIG. 2), the rocket motor 300 (FIG. 3), or the nozzle 350 (FIG. 4).Without being bound to any particular theory, the ceramic 404 may formby sintering of the partially cured polymer 104 to remove carbon fromthe solid structure. For example, the carbon of the partially curedpolymer 104 (see FIG. 1) may be removed in the form oflow-molecular-weight organic materials and combustion products of carbon(e.g., carbon dioxide). Gases, such as hydrogen, nitrogen, carbondioxide, or carbon monoxide, may form and diffuse away from the surface402. The reaction of the partially cured polymer 104 may leave a portionof inorganic material (e.g., a layer of inorganic material) over aportion of the fibers 102 or the cross-linked polymeric matrix 106. Theceramic 404 may adhere or cling to the fibers 102 or the cross-linkedpolymeric matrix 106, such that the ceramic 404 remains at the surface402 of the insulation material 400 and provides resistance to heattransfer through the insulation material 400. The ceramic 404 may remainon the surface 402 of the insulation material 400 when exposed to gasturbulence.

The ceramic 404 may have a higher thermal reflectivity (defined as theradiation reflected by a surface divided by the radiation received by asurface) than the cross-linked polymeric matrix 106 or the partiallycured polymer 104. Thus, upon formation of the ceramic 404, which is aglassy material, the insulation material 400 may reflect more thermalenergy than the insulation material 100 (FIG. 1) lacking the ceramic404. Thus, the ceramic 404 may improve the ability of the insulationmaterial 400 to protect surfaces from extreme temperatures.

Returning to FIG. 3, the rocket motor 300 may be used to propel avehicle (e.g., a rocket). The igniter 312 may be activated to ignite theenergetic material 308 within the casing 302. The burning energeticmaterial 308 may heat the interior of the casing 302, including theenergetic material 308, the liner 306, and the insulation material 304.Combustion of the energetic material 308 exposes the insulation material304 to hot gases. For example, combustion of the energetic material 308may form gases at temperatures of about 1200° C. or higher, about 1800°C. or higher, or even about 2400° C. or higher. The gases ablate aportion of the cross-linked polymeric matrix 106 and a portion of thepartially cured polymer 104 forms ceramic 404 (see FIG. 5). The ceramic404 may reflect a portion of the heat back into the interior of thecasing 302, heating the energetic material 308 (thus increasing the burnrate thereof) and maintaining the casing 302 at a lower temperature thanmay be observed absent ceramic formation. The nozzle 350 shown in FIG. 4may offer similar benefits, forming a ceramic over the insulationmaterial 354 as hot gases pass through the nozzle 350, especially nearthe throat, where the highest flow velocity typically occurs. Theceramic may decrease the flow of thermal energy to the outer wall 352 ofthe nozzle 350.

FIG. 6 shows a simplified illustration of an embodiment of insulationmaterial 500. The insulation material 500 has a plurality of fibers 502and 504 formed into cloths or sheets of material. For example, thefibers 502 and 504 may be knit or woven. The fibers 502 and 504 arecoated with the partially cured polymer 104. The fibers 502 and 504 arein the cross-linked polymeric matrix 106.

After the insulation material 500 has been subjected to a hightemperature (e.g., greater than about 850° C.), the insulation material600 shown in FIG. 7 may form. Upon exposure to the high temperature, aportion of the cross-linked polymeric matrix 106 is ablated.Furthermore, a portion of the partially cured polymer 104 reacts orfuses to form a ceramic 602 over or around the fibers 502 and 504. Theceramic 602 provides additional insulative properties to the insulationmaterial 600. The ceramic 602 may form a continuous layer over thefibers 502 and 504.

The formation of the ceramic over an insulation material during a rocketmotor firing may be beneficial because the ceramic may have a highervolume or thermal resistivity than the insulation material from whichthe ceramic forms. Formation of ceramic may also limit or preventablation of the insulation material by reflecting heat because theceramic may be more reflective than the cross-linked polymeric matrix106.

Ceramic materials in general may function well as insulators. However,insulation materials containing ceramics tend to be relatively expensiveand have less robust physical properties (e.g., may be more brittle)than other insulation materials. Forming a ceramic material from apartially cured polymer during use and operation of the article (e.g.,during exposure to heat, such as in a rocket motor firing) may providethe benefits of having a ceramic material in the insulation material,yet may limit or minimize problems associated with the ceramic materialbeing present in the insulation material initially. For example, forminga ceramic during use may limit the risk that the ceramic will be damaged(e.g., cracked) during manufacturing or handling of an article. Anydamage to the ceramic during use may be healed by subsequent formationof additional ceramic material. Thus, insulation materials havingpartially cured polymers therein may have better insulating propertiesthan conventional materials.

By increasing the thermal performance of an insulation material, thevolume of the insulation material may be reduced in comparison toconventional insulation materials, leaving a larger volume of thearticle available to contain energetic or other materials. All otherfactors being equal, the performance of a rocket motor may be increasedby increasing the volume of energetic material. The volume of energeticmaterial may be increased by replacing a portion of non-energeticinsulation material with energetic material, so long as the remaininginsulation material provides sufficient thermal protection.

Furthermore, by coating the fibers with preceramic polymers as describedherein, the amount of partially cured polymers and ceramic material mayaccount for a small portion of the insulation material, saving on costsand insulation weight. Since the ceramic material is present as acoating on the fibers, the ceramic material may contribute only a smallamount to the overall weight to the insulation material and, thus, tothe cost of the insulation material.

Because the coated fibers disclosed herein may be used in a matrix ofvarious insulation materials, the matrix may be selected to have a longuseful life (e.g., by retaining physical properties in storageconditions). Lifecycle costs may be decreased by increasing the lifetimeof the insulation material, which further decreases the costs ofproduction (e.g., of replacement components), logistics, and disposal(e.g., of old, unusable components).

The insulation materials disclosed herein may enhance safety of handlingand use of energetic compositions and related components. The insulationmaterials disclosed herein may be used in conjunction with any energeticcomposition, such as solid propellants, gas generators, smokelesspowders, explosives, igniters, etc. The insulation materials may provideprotection from degradation of the casing or other enclosure during theuse of the energetic composition, which may be valuable in protectingagainst catastrophic failure.

The insulation materials may be used as a drop-in replacement forconventional insulation materials in the production of rocket motors andother devices. For example, the insulation material may be used inautomotive air-bag deployment systems, fire walls, fire-fightingequipment, etc. The insulation materials may be particularly useful forprotecting from extremely high temperatures for short periods of time.

The following examples serve to explain embodiments of the insulationmaterials and methods of forming the insulation materials in moredetail. These examples are not to be construed as being exhaustive orexclusive as to the scope of the disclosure.

EXAMPLES

Materials mentioned in the following Examples are available from thecommercial sources indicated, including The Dow Chemical Company(Midland, Mich.), E.I. du Pont de Nemours and Company (Wilmington,Del.), Akrochem Corporation (Akron, Ohio), Vanderbilt Chemicals, LLC(Norwalk, Conn.), PPG Industries, Inc. (Monroeville, Pa.), CabotCorporation (Boston, Mass.), Horsehead Corporation (Monaca, Pa.), andS.F. Sulfur Corporation (Freeport, Tex.). Percentages in the followingexamples are weight percentages based on the total composition mixture.The ingredients of these examples are also summarized in Table 2 below.

Insulation materials were tested using the Plasma Torch Test Bed (PTTB)at NASA's Marshall Space Flight Center. The PTTB includes a plasma torch(Model 7 MB, available from Metco) attached to a mechanical beam or arm.For each test, a square of insulation to be tested was prepared havingdimensions of about 5.1 cm by about 5.1 cm. A heat flux gauge was placedadjacent the square of insulation, and was used to calibrate the torchon each test. A water-spray fume hood in the test bay was configured totrap any noxious gases produced during the test.

The test included weighing and measuring the thickness of the insulationbefore placing the insulation in a sample holder. The plasma torch wasdirected toward the heat flux gauge to measure the heat output of thetorch. The torch was then adjusted as necessary (e.g., by changing thedistance from the torch to the gauge or the amount of fuel or airentering the torch) to obtain a selected flux. Once the appropriate fluxwas obtained, the torch was moved over the insulation sample, e.g., inthe same plane as the heat flux gauge. After exposure to a selected heatflux for a selected period of time, the insulation material was cooled,the ash or ablated material was removed, and the remaining insulationmaterial (including the char) was weighed and its thickness measured.The char was then removed, and the weight and thickness measurementswere repeated. The testing method and apparatus are described in R. E.Morgan et al., “Non-Asbestos Insulation Testing Using a Plasma Torch,”AIAA Paper 2000-3317 (American Institute of Aeronautics and Astronautics2000).

A summary of the silica-filled EPDM (SFEPDM) insulation materials formedand tested in the PTTB is shown in Table 1.

TABLE 1 Insulation materials tested in Examples Change in Flash Exam-thickness ob- ple Insulation type (mils) served? 1 SFEPDM without fibers1 No 1 SFEPDM without fibers 2 No 2 SFEPDM with carbon fibers −2 No 2SFEPDM with carbon fibers 0 No 3 SFEPDM with graphite fibers 0 No 3SFEPDM with graphite fibers 0 No 4 SFEPDM with KEVLAR ® fibers 4 No 4SFEPDM with KEVLAR ® fibers 1 No 5 SFEPDM with coated carbon fibers −3No 5 SFEPDM with coated carbon fibers 11 Yes 6 SFEPDM with coatedgraphite fibers 33 Yes 6 SFEPDM with coated graphite fibers −1 No 7SFEPDM with coated KEVLAR ® fibers 19 Yes 7 SFEPDM with coated KEVLAR ®fibers 8 Yes

Example 1

SFEPDM Insulation without Fibers

A sulfur-cured insulation material (silica-filled EPDM) was formedhaving the composition shown in Table 2.

TABLE 2 Composition of silica-filled EPDM Material Trade Name SourceWeight % ethylene-propylene-diene terpolymer NORDEL ™ IP 4640 Dow Chem.33.05 (EPDM) ethylene-propylene-diene terpolymer NORDEL ™ IP 4520 DowChem. 26.44 (EPDM) chlorosulfonated polyethylene HYPALON ® 20 DuPont6.61 thermoplastic-phenolic resin-tackifier AKROCHEM ® P-133 AkrochemCorp. 3.30 octylated diphenylamines AGERITE ® STALITE ® S VanderbiltChem. 1.32 amorphous silicon dioxide HI-SIL ™ 233 PPG Industries 23.46carbon black HAF Carbon Black Cabot Corp. 0.33 zinc oxide KADOX ® 930Horsehead Corp. 2.64 magnesium oxide ELASTOMAG ® 170 Akrochem Corp. 0.33mercaptobenzothiazole disulfide ALTAX ® MBTS Vanderbilt Chem. 0.99(1,1′(hexadithiodicarbonothioyl)bis- SULFADS ® Vanderbilt Chem. 0.20piperidine) bis(dibutylcarbamodithioato-S,S′) zinc BUTYL ZIMATE ®Vanderbilt Chem. 0.99 sulfur Laccofine Sulfur S.F. Sulfur Corp. 0.33

The insulation material was mixed by hand, spread into a sheetapproximately 3 mm thick, then cured in a press for 60 minutes at about150° C. The cured insulation material was measured and tested in thePTTB under a heat flux of about 600 BTU/ft²s (about 6,800 kJ/m²s). Theplume of gases directed at the insulation material in the PTTB includedalumina particles at a mass concentration of about 0.03%.

The PTTB test was performed in duplicate. After the tests, the thicknessof the insulation was measured, and the insulation materials were foundto be 1 mil (0.001 inch or 0.025 mm) and 2 mils (0.002 inch or 0.051 mm)thicker, respectively, than before the tests. During a typical test, thethickness of insulation can increase due to swelling of insulationmaterial and the formation of char or ceramic. The thickness candecrease due to ablation of the surface of the insulation material bythe plume. The measurement of the change in thickness indicates thecombined effect of these factors.

Example 2

SFEPDM Insulation with Carbon Fiber Cloth

The insulation material of Example 1 (before curing) was applied overand around a carbon-fiber fabric tape (available from Fiberglass Supply,of Burlington, Wash.). The insulation material was cured and tested induplicate as described in Example 1.

After the tests, the thickness of the insulation was measured. Onesample of the insulation materials was found to be 2 mils thinner thanbefore the tests. No change in thickness was observed for the othersample.

Example 3

SFEPDM Insulation with Graphite Fiber Cloth

The insulation material of Example 1 (before curing) was applied overand around a graphite-fiber cloth (available from Fiberglass Supply).The insulation material was cured and tested in duplicate as describedin Example 1.

After the tests, the thickness of the insulation was measured. No changein thickness was observed for either sample.

Example 4

SFEPDM Insulation with Aramid Fiber Cloth

The insulation material of Example 1 (before curing) was applied overand around an aramid-fiber (KEVLAR®) cloth (available from FiberglassSupply). The insulation material was cured and tested in duplicate asdescribed in Example 1.

After the tests, the thickness of the insulation was measured. Theinsulation materials were found to be 4 mils and 1 mil thicker,respectively, than before the tests.

Example 5

SFEPDM Insulation with Coated Carbon Fiber Cloth

A carbon-fiber fabric tape (available from Fiberglass Supply) was coatedwith a silicon carbide preceramic polymer (STARPCS® SMP-10, availablefrom Starfire Systems, of Schenectady, N.Y.) by applying the siliconcarbide preceramic polymer over the cloth, draining the excesspreceramic polymer, and heating the cloth in an oven maintained at 150°C., less than 5 torr, and less than 10% relative humidity for 60minutes. The heating formed the preceramic polymer into a cross-linkedsilicon carbide polymer coating over the cloth. The insulation materialof Example 1 (before curing) was applied over and around the coatedcarbon-fiber cloth. The insulation material was cured and tested induplicate as described in Example 1.

In one test, a flash was observed, in which the energy of the plasmatorch was reflected from the surface of the insulation. Without beingbound to any particular theory, it is believed that the flashcorresponded to formation of a ceramic surface over the insulationmaterial. After the tests, the thickness of the insulation was measured.The insulation material in the test having the flash was found to be 11mils thicker than before the test. The insulation material in the testwithout a flash was found to be 3 mils thinner than before the test.

Without being bound to any particular theory, it is believed thatinsulation materials that did not exhibit a flash may have been deformedin the PTTB apparatus such that the heat flux was not properly focused.This may have prevented the insulation from reaching a temperature atwhich the ceramic material would have formed. An observed flash appearsto correlate with formation of a relatively thick ceramic. Because thesilicon carbide preceramic polymer forms silicon carbide at temperaturesabove about 850° C., exposure of the insulation materials having coatedfibers to temperatures below 850° C. should not cause the formation ofceramic material.

Example 6

SFEPDM Insulation with Coated Graphite Fibers

A graphite fiber cloth (available from Fiberglass Supply) was coatedwith a silicon carbide preceramic polymer (STARPCS® SMP-10) by applyingthe silicon carbide preceramic polymer over the cloth, draining theexcess preceramic polymer, and heating the cloth in an oven maintainedat 150° C., atmospheric pressure, and less than 10% relative humidityfor 60 minutes. The heating formed the preceramic polymer into across-linked silicon carbide polymer coating over the cloth. Theinsulation material of Example 1 (before curing) was applied over andaround the coated graphite-fiber cloth. The insulation material wascured and tested in duplicate as described in Example 1.

In one test, a flash was observed, in which the energy of the plasmatorch was reflected from the surface of the insulation. After the tests,the thickness of the insulation was measured. The insulation material inthe test having the flash was found to be 33 mils thicker than beforethe test. The insulation material in the test without a flash was foundto be 1 mil thinner than before the test.

Without being bound to any particular theory, it is believed thatinsulation materials that did not exhibit a flash may have been deformedin the PTTB apparatus such that the heat flux was not properly focused.This may have prevented the insulation from reaching a temperature atwhich the ceramic material would have formed. An observed flash appearsto correlate with formation of a relatively thick ceramic. Because thesilicon carbide preceramic polymer forms silicon carbide at temperaturesabove about 850° C., exposure of the insulation materials having coatedfibers to temperatures below 850° C. should not cause the formation ofceramic material.

Example 7

SFEPDM Insulation with Coated Aramid Fibers

An aramid-fiber (KEVLAR®) cloth (available from Fiberglass Supply) wascoated with a silicon carbide preceramic polymer (STARPCS® SMP-10) byapplying the silicon carbide preceramic polymer over the cloth, drainingthe excess preceramic polymer, and heating the cloth in an ovenmaintained at 150° C., atmospheric pressure, and less than 10% relativehumidity for 60 minutes. The heating formed the preceramic polymer intoa cross-linked silicon carbide polymer coating over the cloth. Theinsulation material of Example 1 (before curing) was applied over andaround the coated aramid-fiber cloth. The insulation material was curedand tested in duplicate as described in Example 1.

In both tests, a flash was observed, in which the energy of the plasmatorch was reflected from the surface of the insulation. The insulationmaterials were found to be 19 mils and 8 mils thicker, respectively,than before the tests.

Prophetic Example 8

EPDM Insulation with Coated Aramid Fibers

An aramid-fiber is coated with a silicon carbide preceramic polymer(STARPCS® SMP-10) by applying the silicon carbide preceramic polymerover the cloth, draining the excess preceramic polymer, and heating thecloth in an oven maintained at 150° C., atmospheric pressure, and lessthan 10% relative humidity for 60 minutes. The heating forms thepreceramic polymer into a cross-linked silicon carbide polymer coatingover the cloth. A sulfur-cured insulation material (EPDM) is formedhaving the composition shown in Table 3. The composition shown in Table3 is similar to the composition shown in Table 2, above, but without theamorphous silicon dioxide. Alternatively, the EPDM insulation may beformed with another filler material.

TABLE 3 Composition of EPDM Material Trade Name Source Weight %ethylene-propylene-diene terpolymer NORDEL ™ IP 4640 Dow Chem. 43.19(EPDM) ethylene-propylene-diene terpolymer NORDEL ™ IP 4520 Dow Chem.34.54 (EPDM) chlorosulfonated polyethylene HYPALON ® 20 DuPont 8.64thermoplastic-phenolic resin-tackifier AKROCHEM ® P-133 Akrochem Corp.4.31 octylated diphenylamines AGERITE ® STALITE ® S Vanderbilt Chem.1.72 carbon black HAF Carbon Black Cabot Corp. 0.43 zinc oxide KADOX ®930 Horsehead Corp. 3.45 magnesium oxide ELASTOMAG ® 170 Akrochem Corp.0.43 mercaptobenzothiazole disulfide ALTAX ® MBTS Vanderbilt Chem. 1.29(1,1′(hexadithiodicarbonothioyl)bis- SULFADS ® Vanderbilt Chem. 0.26piperidine) bis(dibutylcarbamodithioato-S,S′) zinc BUTYL ZIMATE ®Vanderbilt Chem. 1.29 sulfur Laccofine Sulfur S.F. Sulfur Corp. 0.43

The sulfur-cured insulation material is applied over and around thecoated aramid-fiber cloth.

Prophetic Example 9

NBR Insulation with Coated Aramid Fibers

An aramid-fiber (KEVLAR®) cloth is coated with a polysilazane siliconcarbide preceramic polymer by applying the silicon carbide preceramicpolymer over the cloth, draining the excess preceramic polymer, andheating the cloth in an oven maintained at 150° C., atmosphericpressure, and less than 10% relative humidity for 60 minutes. Theheating forms the preceramic polymer into a cross-linkedsilicon-nitrogen coating over the cloth. A nitrile butadiene rubber(NBR) is formed having copolymers of acrylonitrile and butadiene, suchas NIPOL® 1042, NIPOL® 1052, NIPOL® 1052-30, NIPOL® 1312, orcombinations thereof, commercially available from Zeon Chemicals(Louisville, Ky.). The NBR is applied over and around the coatedaramid-fiber cloth.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, the present disclosure is not intended to be limited to theparticular forms disclosed. Rather, the present disclosure is to coverall modifications, equivalents, and alternatives falling within thescope of the present invention as defined by the following appendedclaims and their legal equivalents.

1. An insulation material, comprising: a plurality of fibers comprisinga partially cured polymer coating thereon and disposed in a cross-linkedpolymeric matrix.
 2. The insulation material of claim 1, wherein thepartially cured polymer coating comprises an organosilicon polymer. 3.The insulation material of claim 2, wherein the partially cured polymercoating comprises a polycarbosilane.
 4. The insulation material of claim1, wherein the partially cured polymer coating is formulated to form aceramic upon exposure to a temperature of at least about 850° C.
 5. Theinsulation material of claim 1, wherein the cross-linked polymericmatrix comprises a cured solid material.
 6. The insulation material ofclaim 1, wherein the cross-linked polymeric matrix comprises at leastone material selected from the group consisting of polyisoprene,ethylene propylene diene monomer, nitrile butadiene rubber, andhydroxyl-terminated polybutadiene.
 7. The insulation material of claim1, wherein the plurality of fibers comprises at least one of carbonfibers, graphite fibers, and aramid fibers.
 8. The insulation materialof claim 1, wherein the partially cured polymer coating comprises athickness less than a mean diameter of the plurality of fibers.
 9. Theinsulation material of claim 1, wherein the plurality of fiberscomprises a sheet of connected fibers.
 10. A method of forming aninsulation material, comprising: applying a preceramic polymer to aplurality of fibers; heating the preceramic polymer to form a partiallycured polymer over at least portions of the plurality of fibers;disposing the plurality of fibers in a polymeric material; and curingthe polymeric material to form a cross-linked polymeric matrix.
 11. Themethod of claim 10, wherein curing the polymeric material comprisesexposing the polymeric material to a temperature sufficient to crosslinkthe polymeric material without sintering the preceramic polymer.
 12. Themethod of claim 10, wherein disposing the plurality of fibers in apolymeric material comprises encapsulating the plurality of fibers inthe polymeric material.
 13. The method of claim 10, wherein heating thepreceramic polymer to form a partially cured polymer over at leastportions of the plurality of fibers comprises heating the preceramicpolymer to a temperature from about 100° C. to about 300° C.
 14. Themethod of claim 10, wherein curing the polymeric material comprisesmaintaining the polymeric material at a temperature from about 100° C.to about 300° C.
 15. The method of claim 10, wherein applying apreceramic polymer to a plurality of fibers comprises applying apolycarbosilane, a polysilazane, a polysiloxane, or a combinationthereof to the plurality of fibers.
 16. A method of forming a rocketmotor, comprising: coating a plurality of fibers with a partially curedpolymer formulated to form a ceramic upon exposure to a temperature ofat least about 850° C.; disposing the plurality of coated fibers in aninsulation precursor; curing the insulation precursor to form apolymeric matrix without sintering the partially cured polymer; andproviding an energetic material over the polymeric matrix.
 17. Anarticle, comprising: an insulation material over at least one surface ofan article, the insulation material comprising: a plurality of fiberscoated with a partially cured polymer; and the plurality of coatedfibers dispersed in a cross-linked polymeric matrix.
 18. The article ofclaim 17, wherein the insulation material at least partially defines atleast one interior volume, the article further comprising an energeticcomposition disposed within the at least one interior volume at leastpartially defined by the insulation material.
 19. The article of claim18, wherein the energetic composition is selected from the groupconsisting of a propellant composition, a gas generator composition, asmokeless gun powder composition, a munitions composition, and anexplosive composition.
 20. The article of claim 17, wherein the articlecomprises a rocket motor, a rocket motor nozzle, a gas generatingdevice, ordnance, or munitions.